The invention relates to a device for the production of brushes that have a twisted carrier part made from wire sections with a set of bristles and a handle-side and/or a head-side overmolding, with an injection molding tool for holding and for overmolding of the head-side or handle-side end region of a brush pre-form, wherein this tool has a mold part with a passage for the end region.
Such twisted brushes are used, for example, as inter-dental brushes, mascara brushes, or in the medical industry. These have wire sections with a diameter in the range of approximately 0.17 mm to 0.4 mm. During their production, the bristles are first twisted in the wire sections. This brush pre-form provided with bristles is then introduced with its bristle-less head or end region into an injection molding tool, wherein a brush handle or a head-side overmolding is molded. Here it is problematic that the passage must have dimensions that are large enough to be able to insert the carrier part that could have certain tolerances in its dimensions, so that, between the passage and the wire of the carrier part, an intermediate space remains through which injection material can penetrate outward when the injection pressure is too high. Thus, it can be processed only with low injection pressure, wherein, however, the retaining force between the injection-molded end area of the brush and the injection-molded plastic material is limited.
From DE 103 28 445 A1, a device is already known in which the passage between an injection position holding the carrier part of the brush in a clamping and essentially sealing manner and an insertion and removal position releasing the carrier part is variable with an opening cross section enlarged relative to the opening cross section in the injection position. Therefore, the injection pressure can indeed be increased, but cavities still remain between the twisted wire sections and the passage, so that the injection pressure is further limited. Especially for larger brushes, such as pipe-cleaning brushes, for example, for cleaning firearms, pipes, or chimneys, or for bottle-cleaning brushes, but also for larger mascara brushes or certain medical brushes, these cavities are relatively large due to the thickness of the wire sections, so that, in turn, processing can be performed only with low injection pressure.